It is known to make a multitude of electronic microcircuits simultaneously on a wafer by depositing in succession layers of conductive, semiconductive, or insulating material, which layers are etched by chemical etching after selective exposure through a mask that determines which zones are exposed so as to make them sensitive to chemical etching.
Each component of the microcircuit is obtained by a superposition of mutually contacting layers in a given area. In order to obtain high component density and constant performance of the components that are made, it is necessary for the images of the masks used in succession to present high quality, i.e. for the lines in the image to be very fine, with very little distortion so as to enable the successive images used for etching each of the layers to be put very accurately into register.
In order to make electronic microcircuits, it is known to use an exposure device that comprises a radiation source emitting radiation, a reticle formed by a mask that is to be reproduced, the mask being mounted between the radiation source and an optical projection system for shaping the radiation downstream from the reticle, with the optical projection system comprising a series of mirrors and/or lenses for making an image of the reticle.
Given the component density that is now being sought, it is necessary to make images presenting image quality of the order of a few tens of nanometers, and in order to obtain satisfactory registration between the successive images, it is then necessary for distortion to be of the order of a few nanometers.
Given the numerous disturbing factors within the optics, in particular temperature variations that can occur while making the different layers of the microcircuits, and the coefficients of thermal expansion of the materials constituting the support for the optical system, such accuracy can be obtained only if it is possible to compensate for the dimensional disturbances of the optical projection system.
US patent document US 2004/27632 discloses an imaging or exposure device comprising a radiation source emitting radiation, a reticle mounted between the radiation source and an optical projection system for shaping the radiation downstream from the reticle, the optical projection system comprising a series of mirrors for making an image of the reticle, some of the mirrors of the optical projection system being deformable mirrors including deformer members connected to a control unit.